The invention relates generally to medical devices and methods of use in vessels, ducts or lumens of living beings, and more particularly to expandable intraluminal grafts and methods of use within the vascular tree of a living being to revascularize any blood vessel which is occluded (either partially or totally) by intrinsic or extrinsic disease.
Percutaneous balloon intraluminal dilation of vascular stenoses or blockages through the use of an angioplasty balloon catheter have proven quite successful. However, such procedures are not without risk or some drawbacks. In particular, the angioplasty balloon is inflated within the narrowed vessel in order to shear and disrupt the wall components of the vessel to obtain a large lumen. The relative incompressible plaque remains unaltered by this procedure, while the more elastic medial and adventitial layers of the body passageways stretch around the plaque. This process produces subintimal dissection, splitting, tearing, and disruption of the intact intima and wall layers. If the section forms a transverse tear it produces a flap which may lift away from the artery and may produce an obstruction to the lumen, and therefore make the blockage and stenosis worse. In addition, if there is a heavy plaque on one side of the artery wall (as occurs in 80% of atherosclerotic stenotic lesions) the thinner layer may be disrupted by the inflation of the balloon and cause hemorrhage. Moreover, after the balloon is decompressed any loose material may dislodge completely and act as an embolic source to occlude the lumen of the vessel distally to such an acute extent as to result in significant emergency ischemic conditions. This situation has occurred frequently enough to pose a significant risk to the patient.
Laser assisted balloon angioplasty has been used frequently in recent years to revascularize a totally occluded vessel. In particular the occlusion is opened with the laser and then the opening is expanded further by balloon angioplasty. One of the problems with this revascularization procedure is that the laser causes intimal damage along with the balloon. Moreover, this procedure has only been useful for short segment occlusions. When long segment occlusions are attacked by this procedure the reocclusion rate has proven to be very high, and sometimes even made worse.
In both simple balloon angioplasty and in laser assisted balloon angioplasty there is a high incidence of recurrence of the stenosis or obstruction. This is, of course, in addition to the risk of embolization and acute occlusion and disruption of the artery with massive hemorrhage. In addition, there are certain vessels bearing areas of plaque which are not amenable to balloon angioplasty because of the fact that they are orificial plaques, i.e., plaques at the orifice of a branch artery. Thus, when the balloon is inserted across this type of lesion and inflated, it inflates differentially, that is the portion of the balloon in the larger part of the artery inflates more than the portion of the balloon crossing the narrowed or stenotic segment. In fact the portion of the balloon crossing the narrowed or stenotic segment frequently does not inflate at all. Therefore, unsuccessful attempts at inflation are the rule rather than the exception. This is particularly true in attempting the revascularization of renal arteries or the superior mesenteric artery.
Intraluminal endovascular grafting has been demonstrated by experimentation to present an alternative to conventional vascular bypass surgery. Such "grafting" involves either the percutaneous insertion into a blood vessel of a tubular prosthetic graft or stent or an open insertion thereof through a short segment exposed portion of the blood vessel. The graft is typically positioned in a predetermined location within the blood vessel and then expanded by a catheter delivery system. However, the use of conventional bypass grafts exhibits the tendency of recurring stenosis. Such restenosis may progress to the point where the graft fails. In this connection the cause of stenosis in bypass grafts (including dialysis access fistulas) is usually fibro-intimal hyperplasia (also known as pseudo-intimal hyperplasia or neo-intimal hyperplasia), a very elastic fibrous tissue which recollapses almost immediately upon relaxation of the balloon. Such tissues are, however, ideal for being supported by a stent (i.e., a self supporting member).
Accordingly, it has been suggested, and there is some activity now occurring, to use stents in revascularization procedures to preclude restenosis. Another useful area of stent application is percutaneous angioplasty of Takayasu arteritis and neurofibromatosis arterial stenoses, since those conditions may show poor response and recurrance which is very high due to the fibrotic nature of these lesions.
The stent devices which have been used for the foregoing procedures have included cylindrical springs of stainless steel, sleeves of expandable heat sensitive material, and expandable sleeves formed of linked stainless steel wires arranged in a zig-zag configuration. The problems with these devices is there is no effective control over the final expanded configuration of each structure.
As will be appreciated by those skilled in the art the expansion of a coiled spring type stent is predetermined by the spring constant and the modulus of elasticity of the particular material making up the spring. These same factors predetermine the amount of expansion of the zig-zag stainless steel wire stents. In the case of an intraluminal stent formed of a heat sensitive material, which expands on heating, the amount of expansion is likewise predetermined by the heat expansion characteristics of the particular alloy utilized in the manufacture of the device. Therefore, once these expandable sleeve-like devices are inserted into the lumen their size can change. Moreover, if there has been a miscalculation in the size of the fit, an undersized stent may not expand enough to become impacted into the arterial wall for securement thereto, thus allowing it to migrate or move from the desired position and possibly even cause embolic occlusion distal to the point of insertion. An oversized graft may cause rupture of the arterial wall or tear in the plaque at the ends of the graft, producing a dissection point.
Therefore, there is an element of significant risk in the use of the prior art stent devices for revascularization of occluded arteries. Moreover, and perhaps more significantly another problem with the use of prior art devices for revascularization procedures, however, is the fact that such devices are mesh-like or otherwise open or perforated and hence susceptible to scar tissue ingrowth. Another problem with such stents is their relative rigidity. This factor requires them to be used for short occlusive lesions, since they are unable to follow the natural curves of the vessel.
Examples of various types of expandable grafts/stents are disclosed in U.S. Pat. Nos. 4,047,252 (Liebig et al), 4,503,569 (Dotter), 4,580,568 (Gianturo), 4,733,665 (Palmaz), 4,740,207 (Kreamer), 4,776,337 (Palmaz), 4,795,458 (Regan), and 4,856,516 (Hillstead), and in the following literature: "Balloon-Expandable Intracoronary Stents in the Adult Dog", Circulation, Aug. 1987, pages 450-456, Vol. 76, No. 2; "Normal and Stenotic Renal Arteries: Experimental Balloon-expandable Intraluminal Stenting", Radiology, 1987, pages 705-708, Vol. 164, No. 3; "A Titanium-Nickel Alloy Intravascular Endoprosthesis", Transactions American Society of Artificial Internal Organs, 1988, pages 399-403, Vol. XXXIV; "Self-Expanding Endovascular Stent in Experimental Atherosclerosis", Radiology, Mar. 1989, pages 773-778, Vol. 170, No. 3; "Emergency Stenting for Acute Occlusion After Coronary Balloon Angioplasty", Circulation, Nov. 1988, pages 1121-1127, Vol. 78, No. 5; "Intravascular Stents for Angioplasty", CARDIO, Dec. 1987; " Intra-Arterial Stenting in the Atherosclerotic Rabbit", Circulation, Sept. 1988, pages 646-653, Vol. 78, No. 3; "Intravascular Stents to Prevent Occlusion and Restenosis After Transluminal Angioplasty", The New England Journal of Medicine, Mar. 1987, pages 701-706, Vol. 316, No. 12; "A Polyester Intravascular Stent for Maintaining Luminal Patency", Texas Heart Institute Journal, Nov. 1, 1988, pages 12-16, Vol. 15. "Post Dilatation Stenting; Early Experience of the Use of an Endocoronary Prosthesis to Prevent Restenosis Recurrance After Angioplasty", J. Cardiovasc. Surg. 28, 1987, Session 8: CARDIAC-CORONARY (II); "Intravascular Stents to Prevent Occlusion and Restenosis After Transluminal Angioplasty", Abstract from New England Journal of Medicine 1987, Volume 316, pages 701-706; "Vascular Stenting in Normal and Atherosclerotic Rabbits", Circulation, Feb. 1990, Vol. 81, No. 2, pages 667-683; Treatment of Major Venous Obstruction with an Expandable Endoluminal Spiral Prosthesis, J. Cardiovasc. Surg. 30, 1989, pages 112-117; and Venous Stenases in Dialysis Shunts: Treatment with Self-Expanding Metallic Stents, Radiology, Feb. 1989, Vol. 170, No. 2, pages 401-405.
Accordingly, the need exists for an expandable intraluminal vascular bypass graft and methods of use which overcomes the disadvantages of the prior art, e.g., can be used over long distances, for long segment occlusions in the vascular tree, while acting to prevent acute and chronic recurrence.